There are numerous studies that demonstrate that the accumulated plaque at the enamel-gingival junction significantly increases the severity of the gingival disease, while other studies show that when plaque is removed, healthy condition is reestablished. Because of the apparent direct cause and effect relationship between plaque and gingival inflammation, it is widely believed that plaque accumulation is detrimental to gingival health.
It has been suggested that if the accumulation of plaque at the enamel-gingival junction can be prevented or at least retarded, the severity of gingivitis and periodontitis can thereby be reduced.
Compton and Beagrie (Journal of Clinical Periodontology:1975:2:33-43) tested the effectiveness of a quaternary ammonium compound, benzethonium chloride, and zinc chloride in preventing plaque and gingivitis. The above two agents were tested separately and also in combination. According to the authors, the results showed no significant differences in the gingival scores after a ten day test period during which the results of using mouthwashes comprising 1 part glycerine to 20 parts of water and containing (a) 0.22% by weight ZnCl.sub.2, (b) 0.075% benzethonium chloride, and (c) a combination of the two were compared to the results with the placebo treated group. Use of the mouthwash containing the benzethonium chloride alone was found to result in about 42% less plaque formation after the 10 day period than did use of the placebo, the combination, or the ZnCl.sub.2 only mouthwashes. Thus the zinc chloride alone was ineffective as a plaque inhibitor, too. In the late forties, the combination of zinc chloride with potassium ferro-cyanide was tried for the prevention of tooth decay with varying results. (Positive results were reported by Gillard et al in The Journal of the Houston District Dental Society, Vol. 21, No. 3, pp. 2 and 3, March, 1949. Negative results with the same combination were reported by Ast et al in The Journal of the American Dental Association 41(4):437-442, October, 1950. No mention was made in either article of any effect of zinc chloride or the combination on gingivitis.)
Zinc chloride, in high concentrations, 8 to 40%, has been used as an astringent to achieve gingival retraction (Oral Research Abstracts Vol. 4, No. 3, p. 262 Abstract No. 1754). Loe and Silness, J. Pros. Dent. 13:318-328, March-April, 1963, described a procedure in which cotton strings were soaked in an 8% zinc chloride solution before application. The impregnated strings were forced to the bottom of the gingival pockets, by means of a thin steel instrument, and left in place for 10 minutes. Histological studies showed that the 8% zinc chloride-impregnated cotton strings necrotize the epithelial cuff and the adjacent layer of the subepithelial connective tissue.
Zinc chloride-containing antiseptic preparations have been widely used in the past. It is stated in "Accepted Dental Therapeutics" 1971/1972, 34th Edition, p. 200 that zinc chloride has antiseptic, astringent and escharotic activities. At concentrations of 1:2000 (0.05%) to 1:500, (0.2%) a zinc chloride solution has a weak antiseptic action. The authors conclude that "daily use of a mouthwash containing zinc chloride for so-called oral hygiene cannot be considered rational."
Schmid et al, in an article entitled "Effect of a Zinc Chloride Mouthrinse on Calculous Deposits Formed on Foils", Helvitica Odontologica Acta, Vol. 18(1):22-24, 1974, reported that a 0.2% zinc chloride-containing mouthrinse, when administered twice daily over a one week period, significantly inhibited the formation of calculus deposits collected from foils attached to lower incisors.
Gafar et al, Dental and Oral Biology Abstracts, Vol. 54(5)2370, No. 24644, reported that, after the mechanical removal of calculus from teeth, fluoride should be applied to teeth, and an anti-inflammatory treatment with zinc chloride should be applied to the gums.
In U.S. Pat. No. 4,022,880, issued May 10, 1977 to L. J. Vinson and L. P. Cancro, an improved composition for inhibiting dental plaque and calculus formation is disclosed, which comprises a combination of zinc ions and a non-toxic, organoleptically acceptable antibacterial agent. It is taught by the patentees at column 4, lines 1-16, that the use of a zinc compound alone, while affording some anticalculus action, would not produce the desired effect. They disclose, further, at column 4, lines 20-28, that zinc compounds alone or antibacterial agents alone provide only about one-half the protection against dental calculus development as do the compositions claimed in that patent.
Hanke, Jour. A.D.A, Vol. 27, No. 9, September, 1940, pp. 1379-1393, in Table 1, on pages 1384-5, indicates that various concentrations of zinc acetate, lactate and salicylate in 15% glycerol do not have bactericidal effectiveness. However, at page 1388, the author indicates that the use of a zinc acetate solution as a mouth rinse will cause plaque to disappear from even unbrushed teeth, although it is not effective in all cases and the solution appears to lose effectiveness on aging.